Study on the Process of Chromium-Free Chemical Conversion Coating of 7075 Aluminum Alloy

To replace the traditional Alodine chemical conversion coating on aircraft, this paper uses potassium fluotitanate and potassium fluorozirconate as main salts, potassium permanganate as an oxidizing agent and coloring agent, acrylic acid as a complexing agent, and magnesium sulfate as a promoter to prepare a chromium-free environmentally friendly chemical conversion coating on 7075 aluminum alloy. Methods such as drop test, electrochemical analysis, electron microscopy, and elemental analysis were used to determine the optimal film-forming formula and process conditions through single-factor experiments and orthogonal experiments: 6 g/L K₂TiF₆, 6 g/L K₂ZrF₆, 4 g/L KMnO₄, 10 mL/L acrylic acid, 2 g/L MgSO₄; pH 3.7, temperature 35°C, film formation time 6 min. The resulting conversion film is golden yellow, with significantly improved corrosion resistance. This paper also adopts a chromium-free pre-clean instead of the traditional triacid deoxidation pre-clean, achieving chromium-free throughout the entire production process. This has significant guiding implications for future practices in environmental protection in aircraft surface treatment processes.